The present invention relates to a method for manufacturing a microstructure by using a high energy light source; and, more particularly, to a method for manufacturing a microlens or a microstructure having a predetermined pattern by using synchrotron radiation.
Recently, high energy synchrotron radiation has been widely used in the field of X-ray lithography in the semiconductor industry and also in manufacturing microstructures by using the so-called LIGA (X-ray deep etching molding) process first developed in Germany in the course of manufacturing a slot nozzle to separate a uranium isotope.
The synchrotron radiation is a high energy light source, tens of thousand times stronger than other light sources. It has a low dispersion due to excellent parallel beam characteristics and also has the continuous energy spectrum and further is a highly clean light source to radiate under high vacuum. Accordingly, a lithographic exposure time can be significantly reduced by way of using the synchrotron radiation, when compared with other light sources. The microstructure having a high aspect ratio can be manufactured by the synchrotron radiation due to its low dispersion characteristic. The synchrotron radiation also can be an optimum X-ray light source in the LIGA method since it can increase the degree of freedom in the selection of a photomask by choosing an appropriate wavelength range therefor.
One of the applications of the LIGA process can be found in the field of a microlens. The microlens is used as an important element in an optical system, wherein the structure of the microlens needs to be controlled so as to obtain desired optical properties.
One of the conventional microlens manufacturing schemes, proposed by N. Moldovan in xe2x80x9cLIGA AND ALTERNATIVE TECHNIQUE FOR MICROOPTICAL COMPONENTSxe2x80x9d, IEEE, page 149xcx9c152, 1997, will now be described with reference to FIGS. 1A to 1D.
As shown in FIG. 1A, a photosensitive material, e.g., (PMMA: polyMethylMethAcrylate), 12 is coated on a substrate 10. Thereafter, an X-ray exposure process is performed using an X-ray photomask 14. The PMMA is often used as the photosensitive material 12 since the transparency of the lens manufactured by the PMMA is about 90% better than those of other prior art plastic lenses and other optical characteristics thereof are also closer to those of a glass.
Thereafter, a cylindrical pattern 16 is obtained by eliminating a portion of the PMMA exposed to the X-ray, as shown in FIG. 1B, by a developing process.
The whole cylindrical pattern 16 is then exposed to a second X-ray of a lower intensity provided through a membrane filter (not shown) located thereabove, as shown in FIG. 1C.
By exposing the pattern 16 to the weaker second X-ray, only a surface portion 16a of the pattern 16 is affected to have a lower glass transition temperature (Tg) than that of the nonexposed portion.
Finally, as shown in FIG. 1D, the cylindrical pattern 16 is heat-treated at a predetermined temperature so that only the affected surface portion 16a of the exposed cylindrical pattern 16 having low Tg melts and deforms to form a microlens 16b having a hemispherical top portion by a surface tension. Here, the diameter of the microlens 16b is determined by the diameter of the original pattern 16, while the height thereof is determined by the heat-treatment temperature and the height and the diameter of the pattern 16.
However, the conventional microlens manufacturing method described above has some drawbacks in that the manufacturing schemes require two X-ray exposure processes together with a developing process, complicating the whole process.
It is, therefore, an object of the present invention to provide a simplified microstructure manufacturing method by using only one X-ray exposure process, without being subjected to a developing process.
In accordance with the present invention, there is provided a method for manufacturing a microstructure by using a high energy light source, which includes the steps of selectively exposing a portion of a photosensitive material to the high energy light source and performing a heat-treatment for melting and deforming only an upper portion of the exposed portion of the photosensitive material.